What vitamins should not be taken together? If you take any medications, you might be aware that some substances interact within the body or interfere with one another, but is this true for vitamins? With many of us taking supplements to support our health and wellness, it can sometimes be confusing to see medical experts disagreeing on the value of some of these dietary boosters. How safe are they? Is there anything we should know? 

We’ve spoken to some medical experts to get their views on which vitamins you might want to avoid combining and how they interact with one another to sometimes cause problems. If you live in a colder climate, we’ve also rounded the best vitamin D supplements to help support you through the winter months.

While we should rely primarily on a healthy, balanced diet to support good health, sometimes we might need to take a vitamin supplement in order to ensure that we are getting enough of a vitamin. This is of particular concern if you have one of the most common vitamin deficiencies.

Dr. Sarah Brewer, a GP and Medical Director of Healthspan(opens in new tab) tells us more about why you might want to take a vitamin supplement. “By definition, vitamins are essential for life as we cannot make them all in the body (e.g. vitamin C) or in sufficient amounts to meet our needs (e.g. vitamin D),” she says. “Diet should always come first, but the National Diet & Nutrition Studies show that significant numbers of people do not get all the micronutrients they need from their food. A multivitamin then acts as a nutritional safety net.”

A review carried out by the Agency for Healthcare Research and Quality(opens in new tab) indicated that multivitamin and mineral supplements might help reduce the risk of cancer development in malnourished individuals, however, this very rarely applies in the USA.  

Dr. Fiona Barry (PhD BSc Lic Ac MBAcC) from Revive Active(opens in new tab) explains that your diet should be the first port of call for vitamins and minerals and that you should only supplement if you have consulted a doctor. “Ideally, all our nutrition should come from our food and there shouldn’t be a need for vitamin supplements. However, for a variety of reasons most of us need to supplement at some point in our lives, this can be due to extra demands on our health or by virtue of our geography. For example, most people living in Ireland and Great Britain are vitamin D deficient for at least half of the year,” she says. “In this technological age, we are constantly ‘on’, leading to chronically high stress levels. This, in turn, leads to poor sleep, poor digestion, less downtime, and less time in nature, all of which impact our ability to absorb nutrients. Supplements can provide a segway to better overall health if used appropriately, but they are not the solution to better health long term.”

While most vitamins come to us neatly packaged as part of a meal, you might want to be careful if you are combining certain vitamins as dietary supplements.

Dr. Brewer says that if the majority of vitamins coexist with each other in food sources, we don’t need to worry too much about combining them to adverse effects. “As all vitamins are found in various combinations in food there is no robust reason why particular vitamins should not be taken together at normal intakes and all vitamins are found in a multivitamin supplement, for example,” she says. “Once you get into the realms of super dosing, however (which I do not advise) then some minerals should not be combined as they can interfere with each other’s absorption.  For example, the risk of copper deficiency is greater when zinc intakes are high. The ideal dietary ratio of copper to zinc is 1:10.”

A review in the journal Nutrition(opens in new tab) highlights that while we don’t know much about the impact caused by vitamin deficiencies, mineral deficiencies show a very clear drop in performance, affecting muscle function and work capacity. 

Dr. Barry encourages caution when combining fat-soluble vitamins E and K, and vitamins B12 and C for proper absorption. “Some vitamin combinations are best avoided, such as Vitamin E and Vitamin K. Vitamin K is sometimes prescribed by doctors to help with blood clotting. Vitamin E increases bleeding time and can therefore counteract the effect of Vitamin K,” she says. “Vitamin C and Vitamin B12 are another pair of vitamins that may be best taken apart as Vitamin C reduces the absorption of Vitamin B12. Often these vitamins are seen in combination in a multivitamin supplement and, if they are, vitamin B12 is usually at quite a high concentration to overcome this.”

A review in Nutrition Reviews(opens in new tab) also mentions that Vitamin E and Vitamin K interactions are not yet understood and impacts are dramatic in some people and not others.